ceiling light still live
- Thread starter ian1888ah
- Start date
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Well, if you cut across neutral and the CPC at the same time, and short them, then you create an imbalance for the other circuits that are still live, so the main RCD will trip.
If you want to cut the conductors without tripping the RCD, then cut them individually.
If you want to cut the conductors without tripping the RCD, then cut them individually.
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I don't understand what your question is - please could you rephrase it?
Edit:
Ah - I think I get it now. You're assuming that by turning off the lighting MCB you are isolating the relevant circuit completely. Not so - you have isolated the phase, but not the neutral, and in most domestic installations the neutral from all circuits are connected at the CU.
Edit:
Ah - I think I get it now. You're assuming that by turning off the lighting MCB you are isolating the relevant circuit completely. Not so - you have isolated the phase, but not the neutral, and in most domestic installations the neutral from all circuits are connected at the CU.
Yes, neutral and earth are at very slightly different potential, shorting them allows a very small current to flow which unbalences the RCD causing it to trip.
If you want to stop this, then as long as you are confident what you are doing, you can disconnect the neutral at the CU while you work on the circuit, otherwise just ensure you do not touch neutral to earth
If you want to stop this, then as long as you are confident what you are doing, you can disconnect the neutral at the CU while you work on the circuit, otherwise just ensure you do not touch neutral to earth
Softus, I had the lighting circuit switched to off and was shortening the wires to install a new light - didnt realise it could still trip the rcd on the consumer unit.
I take it its still ok to wire the new lights in just not let neutral and earth touch?
I take it its still ok to wire the new lights in just not let neutral and earth touch?
OK - circular and crossing postings are making this hard to read now, but the answer is yes: it's ok to wire the new lights in, and if you prevent neutral and earth from touching then the RCD will not trip.
As a suggestion, if you wire in the neutral first then the chances of it touching an earth are reduced.
As a suggestion, if you wire in the neutral first then the chances of it touching an earth are reduced.
Hm, I suspect you're well on the way towards getting confused.
I surmise that the fact there were previously three bulbs is a red herring. Commonly there are three sets of wires, and one of these is connected to the switch - do connect the red from this set to the phase, along with the other two reds, but DON'T connect the black to the other two blacks, because it is the "switched live". To do so would cause a direct short between phase and neutral on the lighting circuit, and would case the MCB to trip whenever you turn on the switch to your new light.
You now need to visit the reference section and follow the wiring diagram. If you didn't note which black wire was previously used as the switched live, then you need to put a meter across each red/black pair, and turn on the switch, to find out.
If you don't understand this, then please ask, but do visit the ref section first.
I surmise that the fact there were previously three bulbs is a red herring. Commonly there are three sets of wires, and one of these is connected to the switch - do connect the red from this set to the phase, along with the other two reds, but DON'T connect the black to the other two blacks, because it is the "switched live". To do so would cause a direct short between phase and neutral on the lighting circuit, and would case the MCB to trip whenever you turn on the switch to your new light.
You now need to visit the reference section and follow the wiring diagram. If you didn't note which black wire was previously used as the switched live, then you need to put a meter across each red/black pair, and turn on the switch, to find out.
If you don't understand this, then please ask, but do visit the ref section first.
You say you had a 3 spotlight strip fitting, and these 3 cables in one hole in your ceiling were terminated onto each spotlight individually? Unlikely . . . Is this the wiring you noted down before removing the old fitting, or are you guessing?ian1888ah said:
If your wiring is normal, there is a switch pair there, and you will need a piece of terminal block to make an extra connection. See for reference to see how its done!
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